msgget(2) - NetBSD Manual Pages

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MSGGET(2)                 NetBSD Programmer's Manual                 MSGGET(2)


NAME

     msgget - get message queue


SYNOPSIS

     #include <sys/types.h>
     #include <sys/ipc.h>
     #include <sys/msg.h>

     int
     msgget(key_t key, int msgflg);


DESCRIPTION

     msgget() returns the message queue identifier associated with key. A mes-
     sage queue identifier is a unique integer greater than zero.

     A message queue is created if either key is equal to IPC_PRIVATE, or key
     does not have a message queue identifier associated with it and the
     IPC_CREAT bit is set in msgflg.

     If a new message queue is created, the data structure associated with it
     (the msqid_ds structure, see msgctl(2))  is initialized as follows:

     +   msg_perm.cuid and msg_perm.uid are set to the effective uid of the
         calling process.

     +   msg_perm.gid and msg_perm.cgid are set to the effective gid of the
         calling process.

     +   msg_perm.mode is set to the lower 9 bits of msgflg.

     +   msg_cbytes, msg_qnum, msg_lspid, msg_lrpid, msg_rtime, and msg_stime
         are set to 0.

     +   msg_qbytes is set to the system wide maximum value for the number of
         bytes in a queue (MSGMNB).

     +   msg_ctime is set to the current time.


RETURN VALUES

     Upon successful completion a positive message queue identifier is re-
     turned.  Otherwise, -1 is returned and the global variable errno is set
     to indicate the error.


ERRORS

     [EACESS]      A message queue is already associated with key and the
                   caller has no permission to access it.

     [EEXIST]      Both IPC_CREAT and IPC_EXCL are set in msgflg, and a mes-
                   sage queue is already associated with key.

     [ENOSPC]      A new message queue could not be created because the system
                   limit for the number of message queues has been reached.

     [ENOENT]      IPC_CREAT is not set in msgflg and no message queue associ-
                   ated with key was found.


SEE ALSO

     msgctl(2),  msgrcv(2),  msgsnd(2)


HISTORY

     Message queues appeared in the first release of AT&T System V UNIX.

NetBSD                          August 17, 1995                              1